1. Technical Field
The present invention relates to an evaporated fuel processing apparatus that processes evaporated fuel generated in a fuel tank by causing an engine to suck the evaporated fuel through an inlet system for combustion.
2. Related Art
An evaporated fuel processing apparatus or an evaporated fuel purging system that processes evaporated fuel generated in a fuel tank is widely used in the related art in order to prevent the evaporated fuel from being discharged into an environment (atmosphere). The evaporated fuel processing apparatus processes the evaporated fuel by causing the evaporated fuel to be temporarily adsorbed on an adsorptive agent in a canister, causing an engine to suck the adsorbed evaporated fuel through an inlet system of the engine for combustion under predetermined operating conditions.
In recent years, an HEV (Hybrid Electric Vehicle) provided with an engine and an electric motor as drive power sources is widely used to improve a fuel consumption rate (fuel cost). Simultaneously, a PHEV (Plug-in Hybrid Electric Vehicle) that achieves a further improvement in terms of the fuel cost by mounting an increased amount of secondary battery, enabling charging of the secondary battery from outside, and extending a range of travelling as an electric vehicle compared with the HEV is now in practical use.
In the HEV and the PHEV (specifically the PHEV), the engine is stopped for a long time, and thus the frequency of a purge of evaporated fuel adsorbed on the canister is reduced. Therefore, discharge of excessive evaporated fuel which cannot be adsorbed by the canister into an environment, or an increase in size of the canister may be required. Accordingly, a so-called direct purge system is proposed. The direct purge system processes evaporated fuel by trapping the evaporated fuel in a sealed fuel tank instead of adsorbing in the canister and sucking the trapped evaporated fuel directly into the engine through an inlet system under predetermined operating conditions. However, a state in which a pressure in the fuel tank is kept at a high pressure for a long time due to accumulated evaporated fuel in the sealed fuel tank is not preferable, for example, in terms of durability of the sealed fuel tank.
Japanese Unexamined Patent Application Publication (JP-A) No. 2014-190241 discloses an evaporated fuel processing apparatus capable of reducing a pressure in a fuel tank. More specifically, the evaporated fuel processing apparatus disclosed in JP-A No. 2014-190241 opens a sealing valve that seals a communicating path between the interior of the fuel tank and a canister under the conditions that a purge operation for sucking the evaporated fuel from the canister into an intake pipe of the engine is executed and the pressure in the fuel tank is relatively high. At that time, the evaporated fuel processing apparatus controls an opening-closing period of the sealing valve such that an open period of the sealing valve is shorter in a state in which the pressure in the fuel tank is high than in a state in which the pressure in the fuel tank is low.
As described above, since keeping the pressure in the fuel tank at a high pressure for a long time is not preferable in terms of the durability of the fuel tank, there is a desire to reduce the pressure in the fuel tank in an as early stage as possible. However, with the evaporated fuel processing apparatus of the related art, if an attempt is made to increase an amount of the evaporated fuel to be sucked by the engine for reducing the pressure in the fuel tank in the early stage, an air-fuel ratio (A/F) of an air-fuel mixture which burns in the engine may vary, and deterioration in emission may result.